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Rotation of a thrown curveball

curveball is a breaking pitch in baseball
thrown with a characteristic grip and hand movement that impart
down and/or sideways spin to the ball. It is therefore considered a type of
breaking ball. Contrary to a fastball
(which has only back spin), the curveball has a diagonal spin that
creates a wake behind the ball, making the pitch drop on its way to
the plate. A curveball is used to disrupt the opponent's timing.
While it is a good pitch for doing so, it is also a dangerous pitch
to throw. The increased topspin of the ball has the potential to
gain tremendous backspin off of a batter's bat, giving it much
added distance if well hit. For pitchers, it is better to throw a
straight breaking ball, one that breaks from high to low as opposed
to side to side. The simple argument for this is that the batter
has 33 inches to hit a side to side pitch, while only one inch to
hit an up to down pitch.

Theory

A fastball typically has backspin, giving it relatively stable aerodynamic characteristics in flight. The spin of a curveball moves in the opposite
direction. This spin causes a curveball to "break", or drop down
and sweep horizontally as it approaches home
plate, thus frustrating the batter.

When throwing a curve, the pitcher creates
downspin by rolling his or her palm and fingers over the top of the
ball while releasing it. The direction of the break depends on the
axis of spin on the ball. There are many variations of the
curveball, but most are described in terms of their movement when
superimposed on a clock. A "12–6" or "overhand" has a more or
less straight downward action as it approaches the plate, while
more sweeping curveballs might be described as "1–7" or "slurves". The slurve is most commonly found in
left-handed pitchers, and rarely right-handed. There is no specific
point where a ball breaks, but the deviation from a fastball
trajectory becomes progressively greater as the ball approaches the
plate. The point of breaking is normally determined by the point at
which the pitcher snaps his wrist. If the wrist is rotated, or
snapped, earlier in the motion the ball will have a more looping or
early breaking trajectory. If the wrist is snapped later in the
motion the ball will hold its path longer and curve later.

Generally the Magnus effect describes
the laws of physics that make a curveball curve. A fastball travels
through the air with backspin, which creates a high-pressure zone
in the air ahead of and under the baseball. The baseball's raised
seams augment the ball's ability to churn the air and create high
pressure zones. The effect of gravity is
temporarily counteracted as the ball rides on and into energized
air. Thus the travel of a fastball is more or less straight, at
least over the distance from the mound to home plate.

On the other hand, a curveball, thrown with topspin, creates a high-pressure zone on top of the
ball, which deflects the ball downward in flight. Combined with
gravity, this gives the ball an exaggerated drop in flight that is
difficult for the hitter to track. The curveball may have some
horizontal movement as well, depending on the tilt of its axis of
spin.

At the professional level, a curveball is usually about 15 miles
per hour slower than a fastball. However, curveball behavior is
unique to each pitcher. Some use a more looping slow curve and some
use a harder, faster slurve. The speed difference between a
curveball and fastball, as well as the curveball's movement, serve
to deceive the batter. Ideally, a curveball will have its greatest
break just as it reaches the plate and cause the batter to swing
above it.

To throw a curveball correctly, proper spin must be given to the
ball as it is released. Generally pitchers grip the ball deeper
into their palm and fingers than they would a fastball. Pitchers
usually position their index finger aside one of the ball's raised
seams for more leverage in spinning the baseball. At the release
point they then roll their hand over the top of the ball to throw
it forward with downspin. If this movement is poorly executed the
ball will have lazy spin, not break in flight, and be much easier
to hit—the "hanging curve".

When thrown correctly, it could have a huge break from seven to as
much as 20 inches .

There has been debate on whether a curve ball actually curves or is
an optical illusion. In 1949, Ralph
B. Lightfoot, an aeronautical engineer at Sikorsky Aircraft, used wind tunnel tests
to prove that a curve ball does in fact actually curve. However,
optical illusion caused by the ball's spinning may play an
important part in what makes curve balls difficult to hit. The
curveball's trajectory is smooth, however the batter perceives a
sudden, dramatic change in the ball's direction. When an object
that is spinning and moving through space is viewed directly, the
overall motion is interpreted correctly by the brain. However, as
it enters the peripheral vision, the internal spinning motion
distorts how the overall motion is perceived. A curveball's
trajectory begins in the center of the batter's vision, but
overlaps with peripheral vision as it approaches the plate, which
may explain the suddenness of the break perceived by the batter.
On whether
a curve ball is caused by an illusion, Baseball Hall of
Fame pitcher Dizzy Dean has
been quoted in a number of variations on this basic premise: "Stand
behind a tree 60 feet away, and I'll whomp you with an optical
illusion!"

A popular nickname for a curveball is the "deuce", since it is
commonly the number 2 pitch in a pitcher's repertoire. Catchers
often use a two-finger signal when requesting the curveball. Other
popular nicknames for the pitch include: "hammer", "bender",
"hook", "yakker", "Public Enemy No. 1", (as coined by the Los
Angeles Dodgers announcer Vin Scully, in
reference to the curve ball of Dodger pitcher Clayton Kershaw and "Uncle Charlie".

There are two types of curveballs: a 12 6 curveball and a 10 4
curveball, with the main differences being in finger
placement.

Injuries

A curveball, because of the risk of injury to the pitcher’s elbow
and shoulder, can be considered a more advanced pitch, geared
towards pitchers with more developed and mature arms. It is
suggested that the pitcher be near 12 to 14 years old before
attempting a curve ball. This restriction is not due to the ability
to learn how to throw a curveball; rather, the restriction is
advised to allow for proper maturity of the pitcher’s arm.

Important factors to consider before learning how to throw a curve:

Has the child hit puberty?

How developed are the child’s muscles and connective tissues,
i.e.—ligaments, tendons, and bones?

Is the pitcher in the middle of a growth spurt?

Has the pitcher been taught the correct mechanics in order to
throw a curveball?

The parts of the arm that are most commonly injured by the
curveball are the ligaments in the elbow, the biceps and the
forearm muscles.

The technique can also influence the likelihood of injury, such as
whether the pitcher snaps their wrist, or twists their arm.